1. Field of the Invention
The present invention is related to the field of containers. In particular the present invention is related to hot-fill containers.
2. Description of the Related Technology
In the past, containers used for the storage of products, such as beverages, were made of glass. Glass was used due to its transparency, its ability to maintain its structure and the ease of affixing labels to it. However, glass is fragile and heavy. This results in lost profits due to broken containers during shipping and storage caused by the usage of glass and additional costs due to the transportation of heavier materials.
Plastic containers are used more frequently today due to their durability and lightweight nature. Polyethylene terephthalate (PET) is used to construct many of today's containers. PET containers are lightweight, inexpensive, recyclable and manufacturable in large quantities.
PET containers are used for products, such as beverages. Often these liquid products, such as juices and isotonics, are placed into the containers while the liquid product is at an elevated temperature, typically between 68° C.-96° C. (155° F.-205° F.) and usually about 85° C. (185° F.). When packaged in this manner, the hot temperature of the liquid is used to sterilize the container at the time of filling. This process is known as hot-filling. The containers that are designed to withstand the process are known as hot-fill containers.
The use of blow molded plastic containers for packaging hot-fill beverages is well known. However, a container that is used in the hot-fill process is subject to additional stresses on the container that can result in the container failing during storage or handling or to be deformed in some manner. The sidewalls of the container can become deformed and/or collapse as the container is being filled with hot fluids. The rigidity of the container can decrease after the hot-fill liquid is introduced into the container.
After being hot-filled, the hot-filled containers are capped and allowed to reside at about the filling temperature for a predetermined amount of time. The containers and stored liquid may then be cooled so that the containers may be transferred to labeling, packaging and shipping operations. As the liquid stored in the container cools, thermal contraction occurs resulting in a reduction of volume. This results in the volume of liquid stored in the container being reduced. The reduction of liquid within the sealed container results in the creation of a negative pressure or vacuum within the container. If not controlled or otherwise accommodated for, these negative pressures result in deformation of the container which leads to either an aesthetically unacceptable container or one which is unstable. The container must be able to withstand such changes in pressure without failure.
The negative pressure within the container has typically been compensated for by the incorporation of flex panels in the sidewall of the container, Traditionally, these paneled areas have been semi-rigid by design and are unable to accommodate the high levels of negative pressure generated in some lightweight containers. Currently, hot-fill containers typically include substantially rectangular vacuum panels that are designed to collapse inwardly after the container has been filled with hot product. These flex panels are designed so that as the liquid cools, the flex panels will deform and move inwardly. The adjacent portions of the container, which are located between, above, and below the flex panels, are intended to resist any deformations which would otherwise be caused by hot-fill processing. Wall thickness variations, or geometric structures, such as ribs, projections and the like, can be utilized to prevent unwanted distortion. Generally, the typical hot-fillable container structure is provided with certain pre-defined areas which flex to accommodate volumetric changes and certain other pre-defined areas which remain unchanged.
An important aspect of creating a container that can withstand the hot-fill process without deformation is to create one with aesthetic. An increase in aesthetic appeal of a container improves sales of the product found within the container. However, certain aesthetic designs are difficult to incorporate into a hot-fill container due to the need to accommodate the negative pressure that occurs during the hot-fill process. Especially difficult is the incorporation of spherical features and certain types of labeling due to typical incorporation of strengthening measures. Therefore, a need exists to develop a hot-fillable container that can incorporate select features without compromising the usage of the features due to the need of strengthening structure.